Resin based composite is currently one of the most popular dental restoratives. Used as a direct restorative material, it displays many beneficial properties such as excellent micromechanical bonding to enamel, polishability and aesthetics. Despite many advances in dentine bonding agents, dentine bonding remains problematic with microleakage and recurrent caries, being frequent clinical sequelae. The open sandwich technique was developed to overcome two problems: deficient bonding of resin composites to dentine, and inadequate strength and fracture toughness of conventional glass-ionomers (GI). GI displayed excellent cavity sealing abilities by virtue of their chemical adhesion to tooth structure. Resin-modified glass-ionomers (RMGI) were developed to improve on the weaknesses of conventional GI during early setting i.e. setting rate, water sensitivity and strength. Recently literature has reported the use of ultrasonic activation to set conventional GI, opening the possibility of improving the initial properties of the material and suitability for use in the open sandwich technique. The aim of this study was to compare microleakage of Ketac Molar, Ketac Molar set by ultrasound (US), Vitremer and Ketac N100 used in the open sandwich technique, with the control of a resin based composite, Filtek Z250. Two hundred Class II cavities were prepared in a hundred caries free, human, molar teeth, with half of the cervical margins placed apical and the rest coronal to the cemento-enamel junction. For each material, twenty restorations were placed for each cervical position. The sandwich materials were placed to fill the interproximal box level with the pulpal floor, and a final two layers of resin composite was then placed to complete the restoration. Restored teeth were stored in a laboratory oven for 7 days at 37 °C; margins were then finished initially with a medium grit Sof-Lex disc and finally with a fine diamond drill. Material groups were separated into two halfs to commence microleakage testing or thermocycling. Thermocycling was conducted for 500 cycles between 5 °C and 55 °C, with a dwell time of 30 seconds. Restored teeth were then covered with nail varnish around the restoration margins, and immersed in 0.5% basic fuchsin solution for 24 hours. They were then cleaned, embedded in clear self-curing acrylic and sectioned 3 times with an Accutom-2 precision saw, at 2 mm intervals. Sections were evaluated using a light microscope under 4 time’s magnification and microleakage scores given as: 0 = no leakage; 1 = < ½; 2 = > ½ distance to the axial wall/pulpal floor; 3 = leakage up to axial wall/pulpal floor. Statistical analysis was undertaken using Analysis of Variance (ANOVA) for the cervical and occlusal microleakage scores; p-values <0.05 were considered significant. The cervical microleakage results of cavity margins in dentine showed that Ketac Molar (US) performed better than Ketac Molar, and Ketac N100 performed better than Vitremer. Results in enamel showed no significant differences. The use of the open sandwich technique effectively reduced microleakage of cervical cavity margins placed in dentine but failed to reduce occlusal microleakage of Filtek Z250. Copyright
Dissertation (MSc(Odont))--University of Pretoria, 2008.